This invention relates to a laminated display window, especially for a handheld electronic device, which is resistant to delamination.
It is desirable to provide a glass display window in a handheld electronic device such a media player or a mobile telephone. A glass window is more resistant to scratching than most plastic windows, and may be more suitable for certain types of touch-sensitive displays.
One way to mount a display window is to provide a lip on the window, so that the window fits into the opening of a bezel, while the bezel captures the lip to retain the window. However, it is difficult to create a glass window with such a lip. Whether the glass is molded with a lip, or ground from a larger piece of glass, there may be stresses in such a piece of glass that make it more susceptible to breakage, either in handling before assembly into the device, or if the assembled device is dropped.
One alternative is to laminate the window glass to a larger transparent substrate, which may be another piece of glass or a suitable plastic. The edges of the larger substrate protrude beyond the edges of the window glass to form the desired lip. However, this alternative is not without other difficulties, including, in particular, the risk of delamination.
Lamination is frequently accomplished using a clear adhesive. However, many adhesives, while having high shear strength, have lower peel strength. Thus, any event, such as dropping of the device, that tends to try to separate the layers at the edges may cause delamination by peeling. This is particularly true if the laminated window structure is deformed at its corner, where the peel strength is lowest. Delamination is undesirable because it may compromise the strength of the laminated window or introduce defects into the visible area of the window, or, if there is a greater degree of delamination, it may create a safety hazard.
It would be desirable to be able to provide a laminated display window with increased resistance to delamination.